package smile

import (
  "errors"
  "log"
  "net/http"
  "sync"
  "time"

  "github.com/gorilla/websocket"
)

const (
  // 允許等待的寫入時(shí)間
  writeWait = 10 * time.Second

  // Time allowed to read the next pong message from the peer.
  pongWait = 60 * time.Second

  // Send pings to peer with this period. Must be less than pongWait.
  pingPeriod = (pongWait * 9) / 10

  // Maximum message size allowed from peer.
  maxMessageSize = 512
)

// 最大的連接ID，每次連接都加1 處理
var maxConnId int64

// 客戶端讀寫消息
type wsMessage struct {
  // websocket.TextMessage 消息類型
  messageType int
  data    []byte
}

// ws 的所有連接
// 用于廣播
var wsConnAll map[int64]*wsConnection

var upgrader = websocket.Upgrader{
  ReadBufferSize: 1024,
  WriteBufferSize: 1024,
  // 允許所有的CORS 跨域請(qǐng)求，正式環(huán)境可以關(guān)閉
  CheckOrigin: func(r *http.Request) bool {
    return true
  },
}

// 客戶端連接
type wsConnection struct {
  wsSocket *websocket.Conn // 底層websocket
  inChan  chan *wsMessage // 讀隊(duì)列
  outChan chan *wsMessage // 寫隊(duì)列

  mutex   sync.Mutex // 避免重復(fù)關(guān)閉管道,加鎖處理
  isClosed bool
  closeChan chan byte // 關(guān)閉通知
  id    int64
}

func wsHandler(resp http.ResponseWriter, req *http.Request) {
  // 應(yīng)答客戶端告知升級(jí)連接為websocket
  wsSocket, err := upgrader.Upgrade(resp, req, nil)
  if err != nil {
    log.Println("升級(jí)為websocket失敗", err.Error())
    return
  }
  maxConnId++
  // TODO 如果要控制連接數(shù)可以計(jì)算，wsConnAll長(zhǎng)度
  // 連接數(shù)保持一定數(shù)量，超過的部分不提供服務(wù)
  wsConn := wsConnection{
    wsSocket: wsSocket,
    inChan:  make(chan *wsMessage, 1000),
    outChan:  make(chan *wsMessage, 1000),
    closeChan: make(chan byte),
    isClosed: false,
    id:    maxConnId,
  }
  wsConnAll[maxConnId] = wsConn
  log.Println("當(dāng)前在線人數(shù)", len(wsConnAll))

  // 處理器,發(fā)送定時(shí)信息，避免意外關(guān)閉
  go wsConn.processLoop()
  // 讀協(xié)程
  go wsConn.wsReadLoop()
  // 寫協(xié)程
  go wsConn.wsWriteLoop()
}

// 處理隊(duì)列中的消息
func (wsConn *wsConnection) processLoop() {
  // 處理消息隊(duì)列中的消息
  // 獲取到消息隊(duì)列中的消息，處理完成后，發(fā)送消息給客戶端
  for {
    msg, err := wsConn.wsRead()
    if err != nil {
      log.Println("獲取消息出現(xiàn)錯(cuò)誤", err.Error())
      break
    }
    log.Println("接收到消息", string(msg.data))
    // 修改以下內(nèi)容把客戶端傳遞的消息傳遞給處理程序
    err = wsConn.wsWrite(msg.messageType, msg.data)
    if err != nil {
      log.Println("發(fā)送消息給客戶端出現(xiàn)錯(cuò)誤", err.Error())
      break
    }
  }
}

// 處理消息隊(duì)列中的消息
func (wsConn *wsConnection) wsReadLoop() {
  // 設(shè)置消息的最大長(zhǎng)度
  wsConn.wsSocket.SetReadLimit(maxMessageSize)
  wsConn.wsSocket.SetReadDeadline(time.Now().Add(pongWait))
  for {
    // 讀一個(gè)message
    msgType, data, err := wsConn.wsSocket.ReadMessage()
    if err != nil {
      websocket.IsUnexpectedCloseError(err, websocket.CloseGoingAway, websocket.CloseAbnormalClosure)
      log.Println("消息讀取出現(xiàn)錯(cuò)誤", err.Error())
      wsConn.close()
      return
    }
    req := wsMessage{
      msgType,
      data,
    }
    // 放入請(qǐng)求隊(duì)列,消息入棧
    select {
    case wsConn.inChan - req:
    case -wsConn.closeChan:
      return
    }
  }
}

// 發(fā)送消息給客戶端
func (wsConn *wsConnection) wsWriteLoop() {
  ticker := time.NewTicker(pingPeriod)
  defer func() {
    ticker.Stop()
  }()
  for {
    select {
    // 取一個(gè)應(yīng)答
    case msg := -wsConn.outChan:
      // 寫給websocket
      if err := wsConn.wsSocket.WriteMessage(msg.messageType, msg.data); err != nil {
        log.Println("發(fā)送消息給客戶端發(fā)生錯(cuò)誤", err.Error())
        // 切斷服務(wù)
        wsConn.close()
        return
      }
    case -wsConn.closeChan:
      // 獲取到關(guān)閉通知
      return
    case -ticker.C:
      // 出現(xiàn)超時(shí)情況
      wsConn.wsSocket.SetWriteDeadline(time.Now().Add(writeWait))
      if err := wsConn.wsSocket.WriteMessage(websocket.PingMessage, nil); err != nil {
        return
      }
    }
  }
}

// 寫入消息到隊(duì)列中
func (wsConn *wsConnection) wsWrite(messageType int, data []byte) error {
  select {
  case wsConn.outChan - wsMessage{messageType, data}:
  case -wsConn.closeChan:
    return errors.New("連接已經(jīng)關(guān)閉")
  }
  return nil
}

// 讀取消息隊(duì)列中的消息
func (wsConn *wsConnection) wsRead() (*wsMessage, error) {
  select {
  case msg := -wsConn.inChan:
    // 獲取到消息隊(duì)列中的消息
    return msg, nil
  case -wsConn.closeChan:

  }
  return nil, errors.New("連接已經(jīng)關(guān)閉")
}

// 關(guān)閉連接
func (wsConn *wsConnection) close() {
  log.Println("關(guān)閉連接被調(diào)用了")
  wsConn.wsSocket.Close()
  wsConn.mutex.Lock()
  defer wsConn.mutex.Unlock()
  if wsConn.isClosed == false {
    wsConn.isClosed = true
    // 刪除這個(gè)連接的變量
    delete(wsConnAll, wsConn.id)
    close(wsConn.closeChan)
  }
}

// 啟動(dòng)程序
func StartWebsocket(addrPort string) {
  wsConnAll = make(map[int64]*wsConnection)
  http.HandleFunc("/ws", wsHandler)
  http.ListenAndServe(addrPort, nil)
}